1. Field of the Invention:
The present invention relates to an abnormal signal detecting device which detects the abnormal state of a device by sampling, at periodic intervals, each cycle of an AC signal.
2. Description of the Prior Art:
In the device for sampling periodical AC signals such as current signals in a power system at constant intervals of each signal cycle (usually 30 degree interval) which performs digital conversion and feeds the data into a digital processing device, there is a possibility that the sampled data will not have a constant periodical property and that the data on both sides of the center of the peak value will not be consistent in view of the characteristics of the current signals.
When three consecutive data signals are the same, there is a possibility of an abnormal state in the sampling circuit or the digital conversion circuit etc.
The conventional test for the operation of a device for sampling such current signals in the power system is performed by switching, the input of the device to the test side and feeding known test signals into the device in order to test the output of the device. However, this method is impractical to test the state of the operation of the device from the precise viewpoint that the input is fed from the test side. Therefore, such method has a disadvantage in that it provides test results of low reliability.